1. Field of the Invention
The present invention relates to gas discharge display devices, and in particular to an improvement in such devices having a control plate with a conductor matrix thereon.
2. Description of the Prior Art
A gas discharge display device having a control plate disposed in the gas envelope between the anode and cathode is known from German OS No. 2,412,869, corresponding to U.S. Pat. No. 3,956,667. The control plate in that device divides the interior of the gas envelope into two chambers which are interconnected by perforations in the control plate. The control plate has rows of conductor runs on one side thereof and columns of conductor runs on an opposite side, with the perforations being disposed at row-column intersections. The conductor runs are positively charged and serve as auxiliary anodes. Gas discharge takes place in the chamber between the cathode and the side of the control plate having conductor rows, while post-acceleration of the ions takes place in the chamber between the side of the control plate having conductor columns and the anode. A luminescent screen is carried on the anode. By energizing one or more of the auxiliary anodes, a wedge-shaped gas discharge volume of plasma is formed between the cathode and the auxiliary anode over the entire conductor row length. By simultaneous activation of one or more of the matrix conductor columns on the opposite side of the control plate, plasma electrons generated in the gas discharge area are drawn through the perforations at the intersection points of the rows and columns into the post-acceleration area and accelerated to the anode. Upon impact at the anode luminescent screen, which may be disposed before the anode, a light point is generated as the image of the activated intersection point of the matrix. By selected matrix activation according to time-varying sequence and intensity, characters and images can be displayed on the luminescent screen.
In order to improve and insure that a wedge-shaped gas discharge will be generated under all operating conditions, it is known from German OS No. 2,643,915, corresponding to U.S. Pat. No. 4,130,778 to divide the plate cathode of the above-discussed device into sub-cathodes in the form of cathode strips disposed parallel to the auxiliary anodes. A group of auxiliary anodes is then associated with each sub-cathode. By energization of the sub-cathodes and simultaneous or sequential energization of the corresponding auxiliary anode group, a wedge-shaped gas discharge area is generated only between the anodes and a specific sub-cathode. The division of the cathode plate and the number of auxiliary anodes associated with each sub-cathode is dependent upon the intended use and operating parameters of the display device, such as the type of gas utilized and the gas pressure in the envelope.
Even with the improvement of U.S. Pat. No. 4,130,778, a problem still exists in eliminating or minimizing background luminosity. Such background luminosity results from the fact that even with the use of sub-cathodes the gas discharge area is not sufficiently narrow to encompass only a single conductor row which has been activated so that some ions are still drawn through matrix perforations in non-energized conductor rows, which are then accelerated by the anode attraction and may blur the image on the luminescent screen.